1. Field of the Invention
The present invention relates to a method of producing a conductive belt, the conductive belt produced by the method, and an image-forming apparatus having the conductive belt mounted thereon.
2. Description of the Related Art
An image-forming apparatus such as a copying machine, a facsimile, a printer, and the like for forming an image by an electrophotographic method or an electrostatic printing method has a conductive belt as a transport belt, a transfer belt, an intermediate transfer belt, a fixing belt, a developing belt, a belt for use in an electrophotographic photoreceptor, and the like.
It is necessary for the conductive belt to have a proper stable volume resistivity. As the method of imparting conductivity to the conductive belt, a method of adding a conductive material such as a metal oxide, carbon black or the like to a polymer material is known. For example, the conductive endless belt using the carbon black as the conductive material thereof is described in claim 8 of Japanese Patent Application Laid-Open No. 2002-132053 (patent document 1).
When the electronic conductive material represented by the carbon black is used, in dependence on the dispersion state of particles of the conductive material, an electric resistance value fluctuates to a very high extent inside the belt and among products. Another problem in the use of the electronic conductive material is that when agglomerates of the electronic conductive material are generated in kneading of polymer materials or in a melt extrusion by an extrusion molder, electric current collectively flows therethrough. As a result, it is difficult to control the electric resistance value of the belt and further a large number of very small projections of the agglomerations are formed on the surface of the belt. For example, when the belt is used as an intermediate transfer belt, an obtained image has an irregularity.
To make the belt conductive with the carbon black and adjust the electric resistance value of the belt to an appropriate value of 1.0×106 to 1.0×1012 Ω·cm, it is necessary to use not less than 10 mass % of the carbon black. When the mixing amount of the carbon black is large, the conductive belt becomes brittle, which may make it impossible to perform extrusion molding. For example, even though the polymer composition is molded in the shape of a belt, the conductive belt is inferior in its durability when it is driven continuously and is thus unsuitable as the belt of an image-forming apparatus. This tendency is conspicuous in a belt containing polybutylene naphthalate resin used as a polymer material, although the extent of the brittleness of the belt is different to some extent according to the kind of the polymer material.
To solve the above-described problems, a resin composition containing the carbon nano-fiber having the DBP oil absorption amount at not less than 150 ml/100 g is disclosed in Japanese Patent Application Laid-Open No. 2006-152131 (patent document 2). In this resin composition, the carbon nano-fiber serving as the conductive material has an excellent dispersibility. Thus agglomerates are not generated and the resin composition has a uniform and high conductivity, although it contains a small amount of the carbon nano-fiber.
A conductive belt was formed in accordance with the producing method described in the example of the patent document 2 by using the polybutylene naphthalate resin as the resin composing the conductive belt. As a result, the following problem occurred.
The carbon nano-fiber having the property described in the patent document 2 was added to the polybutylene naphthalate resin at the rate described in the example to form a compound of a resin composition. A belt-shaped molding was formed from the compound by extrusion molding based on the same principle as that of melt spinning method carried out in the example of the patent document 2. The obtained belt was very brittle and was unsuitable for practical use.
Patent document 1: Japanese Patent Application Laid-Open No. 2002-132053
Patent document 2: Japanese Patent Application Laid-Open No. 2006-152131